The major aim of the proposed study is to define the singular and combined role of diet, physical training and behavior therapy in the treatment of childhood obesity. One hundred five children (84 obese and 21 non-obese) ranging in age from 8-15 years will be recruited for the study. All obese children will satisfy 3 specific obesity criteria: weight for height by age greater than 75% tile, triceps and subscapular skinfolds greater than 80% tile, and percent fat greater than 80% tile. Subjects will be randomized into five groups: non-obese controls, obese controls, diet treatment, exercise treatment, and combined diet and exercise treatment. All three treatment programs will receive weekly behavior therapy. Exercise treatment groups will receive 30 min. of warm-up flexibility exercise, life-time sports activities and weight training 3 days/week. All exercise will be done individually or in small groups with one trained leader/3 subjects. Diet treatment groups will meet with a dietician 1 day/week. The diet program will be modification of the caloric exchange program. The combined diet and exercise treatment will include elements from both the diet and exercise treatments. All three treatments will be designed to result in 1.5 to 2.5 pounds of weight loss/week. Each subject will stay in his/her treatment or control regime for 6 months. All subjects will be tested to determine which treatment has the greatest effect on: body composition, cardiovascular function and metabolism. Each subject will be tested prior to, after 6 months of treatment, and 6 months post-treatment. Cardiovascular functin will be evaluated by measuring: resting and exercise blood pressure, vascular responsiveness to stress and functional work capacity. Body composition will be evaluated by measuring percent body fat, lean body mass and growth. Metabolic function will be evaluated by measuring: fasting and 2 hr post-prandial glucose and insulin levels; the changes in glucose, insulin and growth hormone levels following exercise; the changes in serum aldosterone following upright posture; and fasting triglyceride and cholesterol levels. The results from this study will further our understanding of the mechanisms underlying obesity and will enable us to determine how diet and/or exercise induced weight loss effects the physiological abnormalities of childhood obesity.